Break the chocolate into small pieces and put it in a large bowl with the butter.,Place the bowl over a pan with 1cm of barely simmering water, making sure the bowl doesn't touch the water.,Stir occasionally.,______,Add a pinch of salt to the whites and whisk until they form soft peaks.,When the chocolate is completely melted, remove from the heat, break up the yolks and quickly stir them inches.,In three batches, fold in the egg whites until completely mixed.,Transfer to ramekins and refrigerate for at least four hours.